Dense urban terrain represents the single most hazardous environment for US military forces. Key to stealthy operation in this environment is to be able to maintain communication and situational awareness among cooperating forces. Some communication systems are very effective when operating in such environments and may even be adapted to perform ranging, i.e., distance measurement. On the other hand, GPS navigation is not always available because signal reception to a sufficient number of satellites may be restricted by limited visibility. GPS signal reception is also vulnerable to jamming, and anti-jamming measures are needed to improve the robustness when operating in such conditions.
Emerging Time-Difference-Of-Arrival (TDOA) technologies offer the promise of low cost, low power communication over short to moderate distances. TDOA technologies, which are also called Time-Of-Arrival (TOA) technologies, have characteristics that naturally support high precision ranging and time synchronization measurements between communicating terminals. Such measurements, however, provide only relative positions due to constant movement and variation in circumstances of nodes in a network. Relevant TDOA technologies cannot, by themselves, determine the absolute location and orientation of the cooperating nodes or units in the network.
It is therefore an object of the invention to provide absolute location information for nodes in a network.
It is yet another object to provide absolute location information for some or all nodes in a network when not enough nodes in the network are able or capable of obtaining a sufficient number of signals from GPS signal sources to derive a unique position for the nodes.
A feature of the invention is the synergistic combination of TDOA technologies with GPS technologies to arrive at a precise location for each node in the network.
An advantage of the invention is that otherwise incomplete GPS information received by a node in a network can be used to provide a precise location for all nodes in the network.